Scientific Forecaster Discussion
fxus64 kjan 171110 aaa
Area forecast discussion...updated
National Weather Service Jackson MS
610 am CDT Tue Jul 17 2018
updated for 12z aviation discussion and minor forecast update.
12z taf discussion:
low stratus clouds are reducing ceilings to LIFR/IFR at a few
sites across the area this morning, mainly over east MS. MVFR/IFR
fog has also limited visibility at gtr. Otherwise, VFR conditions
are observed across the region. Most ceiling and visibility issues
should improve by mid-morning with VFR conditions returning.
However, scattered to numerous rain showers/thunderstorms and rain developing over south MS
will cause temporary visibility reductions at times through early
in the day. The focus for rain chances will shift farther north in
the afternoon. /Dl/
tweaked highs down over parts of south MS as showers continue to
fill in across the area this morning. Also made some minor
adjustments to further bump up pops during the morning. Thoughts
from the previous discussion still apply...
Through tonight: we remain locked in a similar pattern to
yesterday, with a few notable differences. What remains the same
is the northwesterly flow in the mid/upper levels and the copious
deep layer moisture over the region. What's different is complexes
of storms made deeper inroads into the forecast area yesterday,
with associated disturbances and remnant boundaries now positioned
farther west. One such disturbance, left over from convection
late last night, was situated over east la/west MS this morning. As it
continues to trek southward, it is expected to spark redevelopment
early in the day mainly for areas south of I-20. In fact, we're
already beginning to see such development take place early this
morning. Later in the day, diurnal heating should lead to the
development of additional convection with more coverage farther
north over the remainder of the County Warning Area. With precipitable water remaining above 2"
across most of the area, locally heavy rainfall/localized flooding
can't be ruled out. In addition, guidance is also suggesting
sufficient deep layer shear may exist for a few storms to produce
strong wind gusts. Tonight, a cold front will begin to move across
the mid south and perhaps into north MS overnight. With upper
level flow remaining perturbed, showers and storms will remain
possible through the overnight hours. Though the front is not
expected to reach the forecast area tonight, we may still see
enough of a decrease in deep layer moisture to decrease rain
chances along the Hwy 82 corridor during the overnight hours.
Once again, we have a somewhat tricky temp/heat index forecast
given the anticipated clouds/precip across the area again today.
Yesterday, we met advisory criteria solidly over roughly the
western 2/3 of the area, with early morning clouds and outflow
limiting east MS to just a few sites meeting criteria briefly.
Today, it appears a larger portion of the area may see heating
limited by clouds and precip early in the day - especially the
southern half of the area. Highest confidence in 105-110f heat
indices being reached is across the arklamiss Delta, where tvr met
criteria as early as 10 am yesterday, and where dewpoints have
been running as high as the low 80s over the past few days. Thus,
we posted a heat advisory for most of our la parishes, our southeast Arkansas
counties, and MS counties mainly along the river from vks north.
Farther east, I wouldn't be surprised to see some sites in
north/central MS meet criteria briefly, but temps aren't expected
to be as high today as convection develops during the day. /Dl/
Wednesday through next monday: throughout most of the mid and
extended portions of the forecast period, troughing aloft will
encompass the East Coast and much of the southeast U.S. While in
the west, very strong high pressure aloft centered near The Four
Corners region, will try to build east into the lower Mississippi
River valley. This will essentially place US under persistent
northwest flow aloft through at least the beginning of next week.
Currently, the best rain chances during the period look to be
Wednesday into Thursday. During this time, a frontal boundary will
be stalled and/or meandering about the forecast area, washing out in
the process. A disturbance or two aloft embedded in northwest flow
aloft, are progged to shift southeast across to just northeast of
the region. This, combined with afternoon heating in the low and
middle 90s will help to spark showers and storms across the forecast
area during the afternoon and evening hours.
Late in the work week, over the weekend, and into next Monday, the
aforementioned mid/upper high is expected to shift deeper into the
lower Mississippi River valley. While northwest flow aloft
persists, this east-advancing high will result in rain chances
mainly being shunted to eastern portions of the forecast area. We
will also have to continually monitor upstream for the potential of
any mesoscale convective system activity either moving through or brushing eastern portions
of the forecast area.
Conditions during this time, Friday through next Monday, currently
look to become rather oppressive across the entire forecast area,
especially along and west of the Mississippi River where highs each
afternoon will flirt with and potentially pass the century mark.
Elsewhere, highs will generally range in the mid and upper 90s, with
dew points still in the 70s. Heat index values areawide will likely
reach and surpass 105, with heat advisories likely being needed for
much of, if not all of, the County Warning Area at some point during this timeframe.
It's also possible along and west of the Mississippi River late
week, that afternoon heat index values could climb above 110, thus
resulting in an excessive heat warning for some western portions of
the County Warning Area. /19/
Preliminary point temps/pops...
Jackson 90 73 92 74 / 75 41 45 22
Meridian 92 74 93 73 / 51 35 52 24
Vicksburg 91 74 91 75 / 63 33 40 16
Hattiesburg 87 73 91 74 / 69 36 60 35
Natchez 89 74 91 74 / 62 31 47 20
Greenville 93 73 90 73 / 56 42 33 13
Greenwood 93 73 91 73 / 59 35 32 13
MS...heat advisory from 11 am this morning to 7 PM CDT this evening
La...heat advisory from 11 am this morning to 7 PM CDT this evening
Arkansas...heat advisory from 11 am this morning to 7 PM CDT this evening